1. Field of the Invention
The present invention relates generally to a cooling device for cooling semiconductor elements which generate a substantial quantity of heat and, in particular but not exclusively, to a compact, easy-to-handle and efficient cooling device for cooling such semiconductor elements by utilization of a change in phase between a liquid phase and a vapor phase of a refrigerant.
2. Description of the Related Art
It is well known that some of the semiconductor elements used in, for example, a computer generate a substantial quantity of heat as the computing speed thereof increases. A cooling device including a fan and a heat sink is generally utilized to cool the semiconductor elements. However, the capability of the cooling device to cool the semiconductor elements has now come to a limitation.
In the case of a large-scale computer, Japanese Laid-open Patent Publication No. 5-315488 suggests a method for emergent supply of a refrigerant, but is silent on the control to be effected with the use of an inverter-controlled refrigerant pump. This publication is also silent on the optimum quantity of the refrigerant.
On the other hand, Japanese Laid-open Patent Publication No. 6-120382 suggests a compact cooling device of a heat-pipe type operable by utilization of the phase change of the refrigerant used. This heat-pipe type cooling device would involve an increase in size or insufficient cooling performance particularly when it is used in cooling highly exothermic semiconductor elements.
In any event, the cooling device utilizing the fan and the heat sink is generally widespread in cooling semiconductor elements that emit a relatively small quantity of heat.
The conventional air-cooling device utilizing the fan and the heat sink is effective to cool a semiconductor of about 70 W. However, when it comes to cooling of a semiconductor element of 150 W or higher, the cooling device tends to become too bulky for it to be incorporated within a rack-type frame structure. On the other hand, the system in which the semiconductor elements are immersed in the refrigerant such as disclosed in Japanese Laid-open Patent Publication No. 5-315488 discussed above, has a problem associated with sealability of a vessel for accommodating the semiconductor elements to be cooled and also a problem associated with a storage capability and handing properties because of the cooling device complicated in structure.
Also, since it is directed to mechanical prevention of an increase of the temperature of the semiconductor elements at the time of emergency and cannot therefore be used repeatedly, there has been a problem in that it cannot be used as an optimum control method. In addition, because of lack of availability of a method of controlling a two-phase condition at an outlet of an evaporator, it has been difficult to construct a proper refrigerating cycle. Yet, it is necessary to provide a refrigerant pump of a different cylinder capacity for a cooling device of a different cooling performance and, therefore, it has been required a relatively long period of time to ascertain the reliability.